The present invention relates to a novel fucosyltransferase and its applications.
Many (glyco)proteins, (glyco)lipids or oligosaccharides require the presence of particular fucosylated structures, in order to exhibit a particular biological activity. E.g., many intercellular recognition mechanisms require a fucosylated oligosaccharide: e.g., in order to be bound by cell adhesion molecules, such as L-selectin, specific cell structures have to comprise fucosylated carbohydrates. Another example for fucosylated structures having a biological function are structures that form the AB0 blood group system. Furthermore, therapeutic (glyco)proteins represent the fastest growing class of pharmaceutical reagents, whereby their pharmacokinetic properties and stability are/is ascribed to their glycans.
Due to their complex nature and inherent chemical properties, the chemical synthesis of glycoconjugates is a major challenge and associated with substantial difficulties. Unlike proteins and nucleic acids, for which automated synthesizers are commercially available, glycans—and let alone glycoconjugates—cannot (yet) be synthesized using a general commercial system. Apart from the requirement to control stereochemistry, the formation of specific linkages remains difficult.
In view of the complexness associated with the chemical or the combined enzymatic/chemical synthesis of glycoconjugates, recent approaches have used glycosyltransferases to enzymatically synthesize (glyco)proteins and (glyco)lipids comprising oligosaccharide residues.
Fucosyltransferases, which belong to enzyme family of glycosyltransferases, are widely expressed in vertebrates, invertebrates, plants and bacteria. They catalyze the transfer of a fucose residue from a donor, generally guanosine-diphosphate fucose (GDP-fucose) to an acceptor, which include oligosaccharides, (glyco)proteins and (glyco)lipids. The thus fucosylated acceptor substrates are involved in a variety of biological and pathological processes.
Based on the site of fucose addition, fucosyltransferases are classified into alpha-1,2-, alpha-1,3/4- and O-fucosyltransferases. Several alpha-1,2-fucosyltransferases have been identified, e.g. in the bacteria Helicobacter pylori and Escherichia coli, in mammals, Caenorhabditis elegans and Schistosoma mansoni, as well as in plants. Most of these enzymes can either not be expressed in an active form in bacterial systems, or cannot use lactose as an acceptor.
In mammals, GDP-Fucose is synthesized in the cytoplasm through de novo synthesis and salvage pathway. With the de novo synthesis, GDP-mannose is converted to GDP-fucose via two enzymes, whilst the salvage pathway utilizes the free cytosolic fucose as substrate. In the cell, GDP-fucose becomes concentrated in vesicles and is recognized by fucosyltransferases as a donor substrate. However, the heterologous functional expression of eukaryotic glycosyltransferases, and in particular fucosyltransferases proved difficult in prokaryotic expression systems. Mammalian and in particular human oligosaccharides such as HMOs are not known from prokaryotic sources, thus making the discovery of glycosyltransferases making these oligosaccharides extremely unlikely.
Since the biological activity of many commercially important oligosaccharides, (glyco)proteins and (glyco)lipids depends upon the presence of particular fucose residues, there is a need in the state of the art to efficiently synthesize or produce glycoconjugates that have the desired oligosaccharide residue(s).